The broad objective of this research is to study the changes that occur in protein metabolism as a result of exercise and to establish the underlying biochemical mechanisms which bring about these changes. During the next five year grant period, we propose research in three general areas: (1) We have found that an acute exercise bout results in a decrease in muscle protein levels and an increase in several free amino acids in muscle. The magnitude of the loss of muscle contractile protein is approximately 10-15% in a matter of only one to two hours and is thus a possible factor in fatigue and exhaustion. The research in this area will be aimed primarily at determining the biochemical mechanism involved, the possible hormonal involvement, and if possible, to determine if these changes have a biological advantage for the animal during exercise. (2) The results of the first two years of this research have shown that endurance training of male rats leads to a general decrease in protein synthesis, an increase in muscle protein degradation, and an increase in amino acid oxidation. These studies will be extended to determine the mechanism causing the increased rate of degradation in trained rats. In addition, previous results have implicated altered testosterone levels of trained male rats as being a factor in altered protein metabolism. Thus, another aspect of this investigation will be to determine the effect of training on protein metabolism in female rats. (3) It has become a somewhat widespread practice for athletes (especially weight lifters) to take anabolic steroids in an attempt to increase muscle mass. Although several studies have investigated the effect of these steroids on protein synthesis in muscle, there has not been a comprehensive study of the effect of these hormones on muscle protein metabolism. Thus, the objective for this research area will be to investigate changes in protein synthesis, protein degradation, and amino acid oxidation in muscle after treatment with anabolic steroids.